1. Field
Aspects of the present invention relate to a light emitting diode and a method of fabricating the same, and more particularly, to a light emitting diode having an ohmic reflective structure, and a method of fabricating the same.
2. Discussion of the Background
Generally, since a nitride of a group-III element, such as a gallium nitride (GaN), an aluminum nitride (AlN), or the like, has excellent thermal stability and a direct transition-type energy band structure, it has been recently prominent as a material for a light emitting device of visible and infrared light. Particularly, blue and green light emitting devices using indium gallium nitride (InGaN) have been utilized in various applications such as a large scale natural color flat panel display, a signal lamp, indoor lighting, a high density light source, a high resolution output system, optical communication, and the like.
Since it is difficult to fabricate a homogeneous substrate on which a nitride semiconductor layer formed of the nitride of the group-III element may be grown, the nitride semiconductor layer is grown on a heterogeneous substrate having a crystal structure similar to that of the nitride semiconductor layer, by a process such as metal organic chemical vapor deposition (MOVCD), molecular beam epitaxy (MBE), or the like. As the heterogeneous substrate, a sapphire substrate having a structure of a hexagonal system is mainly used. However, since sapphire is an electrical non-conductor, it limits the structure of a light emitting diode. Therefore, recently, a method of fabricating a high efficiency light emitting diode having a vertical-type structure, by growing epitaxial layers such as a nitride semiconductor layers on a heterogeneous substrate, such as the sapphire substrate, bonding a support layer to the epitaxial layers, and then separating the heterogeneous substrate using laser lift-off technology, or the like, has been developed. For example, Korean Patent Laid-Open Publication No. 10-2012-0080282 has disclosed a high efficiency light emitting diode having a vertical-type structure.
The high efficiency light emitting diode having the vertical-type structure generally includes a metal reflective layer, such as an Al or Ag reflective layer, disposed beneath a p-type semiconductor layer and having a high reflectivity, and a barrier metal layer protecting the metal semiconductor layer. Since the Al or Ag reflective layer has a relatively high reflectivity, it is often used as a reflective layer in a light emitting diode having a vertical-type structure or a flip-type structure. However, in the Al or Ag reflective layer, it is difficult to accomplish or maintain good ohmic characteristics, and reflectivity is easily decreased due thermal deformation.
Therefore, an ohmic reflective structure having good ohmic contact characteristics and improved thermal stability is needed.